Blastrophysics!Finding Patterns in the Noise2017-10-16T22:13:44Zhttp://blastrophysics.wordpress.com/feed/atom/WordPress.comclairdelunahttps://blastrophysics.wordpress.comhttp://blastrophysics.wordpress.com/?p=2372010-02-18T02:37:58Z2010-02-18T02:37:58Z]]>Never let anyone tell you that all launches are the same. This video merges two of my favorite subjects: rocket launches and atmospheric optics.

Here, the SDO launch occurs at a fabulous viewing angle. The person filming the launch is at the perfect vantage point where the transition to supersonic speed by the rocket corresponds to the appropriate angle for a sundog. Watch the film…

As you can see, the shock travelling out from the rocket as it breaks the sound barrier totally obliterates the cloud that created the sundog. By dissipating the ice crystals in the atmosphere that focused the sun’s rays, the sundog is disrupted. That’s not to say that the water vapor or ice crystals were destroyed, but the precise alignment that focused the light has been modified, causing the sundog to disappear in an instant.

Often people talk about “sonic booms” as things one can only hear. But here is a pristine visual example of that effect. How cool is that!

]]>2clairdelunahttps://blastrophysics.wordpress.comhttp://blastrophysics.wordpress.com/?p=2342010-02-10T14:41:51Z2010-02-10T14:41:51Z]]>The SDO Launch is being covered live on NASA TV. Check it out!!

The Solar Dynamics Observatory (SDO) is the next robotic scientific mission NASA will launch. Currently it is scheduled to launch from Cape Canaveral’s SLC-41 on an Atlas 5 rocket on February 3, 2010 with a one hour launch window (10:53-11:53 a.m. Eastern Time). The mission will nominally last for 5 years. After the success of the SOHO, STEREO, and TRACE missions, having another active solar observatory will be an incredible leap in capability for solar science.

And what a leap! SDO will have the fastest time resolution ever flown for solar imaging: 8 full disk images covering 8 different wavelengths every 10 seconds. This means SDO will generate an absolutely phenomenal amount of data. One major challenge for missions in orbit is finding a way to transmit large amounts of data to the ground. Often, spaceborne instruments are capable of generating much more data, but must choose to produce less so that the data storage and transmission requirements are met.

SDO’s solution to this issue is to place the observatory in a geosynchronous orbit over the White Sands ground terminal in Las Cruces, New Mexico. Geosynchronous orbits are special because the satellite orbits the Earth at the same rate that the Earth itself is rotating. These are the orbits used by the satellites that monitor weather, or provide your satellite TV. In this case, the geosynchronous orbit will allow SDO to have very long continuous communications directly with the ground. Direct link to the ground allows for transmission of more data per second than using data relay satellites. So this orbit absolutely maximizes the transmission rate for SDO.

Why does SDO need so much data? Well, because the mission is designed to perform very precise helioseismology measurements. Seismology, the study of how waves travel through an object, is used on Earth to study tectonic disturbances such as earthquakes and volcanos. For large, deep earthquakes, seismic measurements of such disturbances tell geologists much about the inner structure of the Earth. By using SDO to watch waves travel across the surface of the Sun, helioseismologists hope to gain similar knowledge of what is occuring deep below the Sun’s surface.

In fact, observations made from the ground have already demonstrated the feasibility of such science. But ground based solar observatories have significant disadvantages over orbiting spacecraft. For example, SDO will only experience nighttime twice each year, with each being about 3 weeks long. This means the rest of the year SDO will have non-stop viewing of the Sun, giving solar scientists an unprecedented dataset just as we start a new solar cycle.

In addition, SDO hopes to uncover much more about the solar magnetic cycle. After the long solar minimum we have just experienced, it is evident that our understanding of the Sun’s intrinsic magnetic field is still in its infancy. SDO’s monitoring of the Sun’s complex magnetic structure will give us an opportunity to better understand how it interacts internally and with the rest of the solar system; from sunspots, prominences, and coronal mass ejections from the Sun’s surface to solar wind and auroras experienced here on Earth.

I’m so excited to see what new science this observatory unlocks! Of course it still has to go through that last big leap to get it into orbit. Let’s just hope the rocket doesn’t blow up!

]]>0clairdelunahttps://blastrophysics.wordpress.comhttp://blastrophysics.wordpress.com/?p=2062010-01-17T14:51:46Z2010-01-17T14:50:25Z]]>Here’s a wonderful reference website! This group from the University of Nottingham has a project dedicated to explaining the strange symbols you often see when astronomers and physicists start trying to explain how the universe works. The project, called Sixty Symbols, has created videos that discuss each of the symbols on their site. They’ve finished the original sixty, and are now adding more. (They’re up to 72 – click through to the second page to find the other twelve.)

Strictly speaking, not all of them can fairly be called symbols. Some, like the Star of Bethlehem or Schrodinger’s Cat, are related to events or concepts that can be discussed in the context of the fields of astronomy and physics. Even so, these videos are a great reference for those of us who enjoy explaining the universe. Expect to see links to Sixty Symbols in future posts.

And let’s give these guys some traffic!

]]>0clairdelunahttps://blastrophysics.wordpress.comhttp://blastrophysics.wordpress.com/?p=2022010-01-16T21:30:46Z2010-01-16T20:49:55Z]]>A ninja weapon? A game show filled with celebrities?

Nah…this Wheel of Stars is soooo much cooler, and much more pleasant to listen to. It’s a webapp that plays the stars, literally!

As each star passes the meridian, the application plays a tone. The note is based on the star’s color and the volume is based on brightness. The result is an ethereal music of the spheres that you can enjoy while relaxing and surfing the interwebs. And since the whole sky takes 24 hours to rotate around, it sounds different every time!

The stellar positions, colors, and magnitudes (apparent brightness) used in the project were recorded by Hipparcos, a mission that ended in 1993. This just shows how the information such observatories provide can be used for many years to come, and not simply for scientific purposes!

What a lovely work of art…

]]>0clairdelunahttps://blastrophysics.wordpress.comhttp://blastrophysics.wordpress.com/?p=1862009-12-24T21:15:33Z2009-12-24T20:53:14Z]]>It looks like the WISE observatory is happily working through the early checkout phase. During the first few days/weeks of a mission, the engineers verify the basic functionality of a newly launched spacecraft, essentially making sure nothing broke during the extreme environment associated with launch.

During launch, the observatory experiences extreme vibration, acoustic, thermal and space (vacuum) environments either simultaneously or in rapid succession. Prior to launch we test each of these individual environments as best we can, but nothing can really prepare for the intensity of the launch. As a result, the post-launch checkout is a very slow, careful process that exercises each bit of spacecraft functionality one tiny step at a time. That way, if anything has broken, it can be identified early, troubleshot, and either recovered, or changed to a redundant piece of hardware. NASA prefers for all spacecraft to be fully redundant (that is, have a spare bit of hardware for everything in case the primary one breaks) but the reality is that full redundancy is cost prohibitive.

Instruments are often not fully redundant. Almost every single instrument on a NASA mission is one-of-a-kind hardware, designed specifically and solely for the science goal of that mission. Instrument designers do their best to provide redundancy where possible. But there are always parts on the instrument that, should they fail, will end the mission for that instrument.

In addition, many missions have hardware that must be deployed. For example, a solar array may need to be driven from a folded to an extended position, or a door may need to be opened to provide a sun-shade to an instrument. For WISE, the sole instrument on board has a cover protecting the cryogenically cooled interior. The cover keeps out water that would freeze to the interior surfaces, possibly obscuring the detectors. This water originates on Earth, but is carried into space on various surfaces of the observatory, such as within the thermal blankets protecting portions of the spacecraft. Once the observatory has had sufficient time in space for the water to have sublimated away (outgas time), the cover can be removed. In this case, the cover deployment currently scheduled for December 29th will be carried out by firing three explosive fasteners.

Should a deployment fail to occur, it can often mean a mission-ending situation. There is no redundancy in the WISE cover (i.e. you cannot remove an alternate cover and get science data). As a result, this is a very critical activity. In addition, ground testing typically does not exercise the firing of pyrotechnics. Rather, the signal used to release the nuts can be tested prior to installation, and the response of the nuts to such a signal can be tested on duplicate hardware. The upshot is that this deployment is likely the first and only time the entire system has ever been tried all together.

It may seem like this is a foolish method, but unfortunately some systems are simply untestable on the ground. Spacecraft engineers work to test such hardware as thoroughly as possible. However, when deployment time comes, we are all holding our breath until the pyros blow correctly and the cover comes off…

]]>1clairdelunahttps://blastrophysics.wordpress.comhttp://blastrophysics.wordpress.com/?p=1792009-12-22T15:30:40Z2009-12-22T15:30:40Z]]>Finally, after much consternation among solar scientists everywhere (okay, that’s a bit of an exaggeration) the Sun has awaked from one of the deepest solar minima in recent history. You can see a total of five, FIVE, active regions in this extreme ultraviolet picture from SOHO:

The SOHO observatory has monitored solar activity since 1995, sitting at the L1 Lagrangian point between the Earth and the Sun. This stable position, four times farther than the Moon’s orbit, offers an unimpeded view of the solar disk. The science return from this observatory has been incredible, drastically increasing our understanding of the star that powers our planet and lives.

This feat is even more amazing considering SOHO’s history. In 1998, a problem on the observatory ended with the failure of all gyroscopes. For a mission designed around the ability to self-stabilize at the L1 gravitational minimum, such a loss seems mission-ending. However, operations engineers learn early that it’s necessary to work with what is available, even though the situation isn’t optimal. In this case, an amazing effort to rescue the SOHO observatory ensued, and the spacecraft engineers devised a method to use the observatory successfully without gyroscopic stabilization.

The extreme environment of space eventually degrades or destroys the spacecraft we launch. But until we are forced to accept that an observatory is irretrievable, operations engineers will work to keep the mission going. As a result, most missions end due to funding cuts, not hardware failure.

Over at PlaneTalking, Ben Sandilands reports on “Delta V,” a joint venture between Virgin Blue and Delta Air Lines. This caught my eye, because “delta-v” means something completely different in mission operations.

For spacecraft in orbit, there are several forces that can alter the trajectory over time. Atmospheric drag slows the spacecraft, causing the orbit to decay. Pressure from the solar wind can push the spacecraft to lower altitudes. Even the gravitational effects from other bodies (most notably the Moon, Sun, and Jupiter) can affect spacecraft orbits. At times it is necessary to modify that orbit to compensate for these effects. This is accomplished by firing the thrusters to change either the altitude or inclination of the orbit. A change in altitude is accomplished by changing the velocity of the spacecraft, hence the term delta-v. Delta is the mathematical symbol for “change in,” and v stands for “velocity.”

Delta-v maneuvers are a regular part of operations management for certain low-earth orbiting satellites. In fact, any spacecraft that requires a particular orientation with respect to the body it is orbiting (like geosynchronous satellites), or that needs to maintain formation flying with other nearby satellites, will need delta-v maneuvers from time to time. The need for regular delta-v maneuvers increases the payload size by necessitating the inclusion of a propulsion subsystem, and increasing the propellent load the satellite must carry. Recent safe-ocean disposal requirements have made propulsion a must on new NASA spacecraft to allow for a controlled de-orbit (as was performed several years ago with TRMM).

Such maneuvers are also used to help guide interplanetary missions to their targets. Small changes in velocity early in the trajectory translate into large shifts in position at the target location. Even a mission with a single destination (like MRO) requires multiple delta-v maneuvers and a skilled navigation engineer. The more complex the flight plan, the more maneuvers will be required. Luckily, when dealing with such large distances, the amount of propellant needed for these adjustments is reasonably small.

In unmanned space missions, a common propellant is hydrazine, which was used in all three missions I have launched. This highly volatile substance ignites immediately upon release, and does not require an oxidizer to produce thrust. So, while you often hear such maneuvers referred to as “burns,” this particular fuel is not actually burning (oxidizing). For missions where delta-v maneuvers are needed solely to de-orbit the spacecraft, the propulsion system is often left “dry,” remaining untested until the mission is complete. This reduces risk that a failure of the system could terminate the mission prematurely.

]]>0clairdelunahttps://blastrophysics.wordpress.comhttp://blastrophysics.wordpress.com/?p=1632009-12-14T14:45:38Z2009-12-14T13:56:14Z]]>Go check out the launch on NASA TV! (Now that the launch is complete, this link is no longer showing the WISE launch. However, you can watch the replay below.)

]]>0clairdelunahttps://blastrophysics.wordpress.comhttp://blastrophysics.wordpress.com/?p=1552009-12-13T15:09:13Z2009-12-13T15:08:46Z]]>The last few minutes of a launch are very critical. It is at this time that systems on the launch vehichle, and (for some missions) the payload, are switched from using an external power source to using their internal batteries. For Delta launches, this switch usually occurs four minutes before launch, and gives the final insight into the complete health of the system. At this point, if any data indicates a possible problem it is necessary to quickly stop the launch.

In mission operations, words that indicate a specific, time-critical action must be very precise. In this situation, the words used by an engineer to the launch director to stop the launch are:

Preparing to launch a multi-million to multi-billion dollar observatory requires practice. So the last six months prior to launch are filled with practices. “Mission rehearsals” that exercise the post-launch and activation process are very complicated, and are run repeatedly by the mission operations team. “Launch rehearsals” that practice the pre-launch process are performed jointly with the launch vehicle operations team several times before launch. During launch rehearsals, one of the hardest things for me to learn was never to say the word “hold.”

Saying “hold hold hold” only has consequences if you say it on the particular communications channel (voice loop) that is connected to the launch operations team, and I never had any reason to be on that loop. Even so, I spend the last few months finding alternative words to use. “Please carry this for me,” rather than “Please hold this.” “Can you wait a minute,” rather than “Can you hold on.” And the list goes on…

It seems like such an innocuous word, hold, until you realize that with that one word you have the power to stop a launch. And right before launch, even a one day delay is a LOT of manpower, and money. But that’s not nearly as painful as the investigation that would follow a failed launch.

You hope you never have to say “hold hold hold.” But if something’s not right, it’s absolutely the right thing to do…